The Voyager Program
NASA's twin interstellar probes, launched in 1977 to exploit a rare planetary alignment, that explored all four outer planets and became the first human-made objects to enter interstellar space.
Events
Launch of the Twin Voyagers
Voyager 2 lifted off on August 20, followed by Voyager 1 on September 5, aboard Titan-Centaur rockets. The launches exploited a rare alignment of the outer planets, occurring once every 176 years, that allowed each spacecraft to tour Jupiter and Saturn and, for Voyager 2, continue to Uranus and Neptune using gravity assists. Each craft carried the Golden Record, curated by a committee led by Carl Sagan, carrying sounds and images of Earth.
Location: Cape Canaveral, Florida, USA
Discoveries at Jupiter
Voyager 1's flyby in March and Voyager 2's in July 1979 revealed active volcanism on the moon Io, the first volcanic activity observed on another world, and evidence of a possible ocean beneath the ice of Europa. The probes also resolved Jupiter's rings and the complexity of its storm systems.
Location: Jupiter
Saturn and Titan
Voyager 1's encounter with Saturn in November 1980 included a close approach to the moon Titan, whose dense orange atmosphere led mission planners to steer the craft through the Saturnian system in a way that ended its planetary tour. Voyager 2 followed with its own Saturn flyby in August 1981, continuing on toward Uranus despite a jammed scan platform.
Location: Saturn
First Encounter with Uranus
Voyager 2 became the first and only spacecraft to visit Uranus, discovering ten previously unknown moons and a magnetic field tilted dramatically off the planet's rotational axis. The flyby remains humanity's only close look at the seventh planet.
Location: Uranus
Neptune and the End of the Planetary Tour
Voyager 2's flyby of Neptune completed the Grand Tour of all four outer planets, revealing the Great Dark Spot and nitrogen geysers on the moon Triton. The encounter was the last planetary visit by either craft before both headed toward interstellar space.
Location: Neptune
The Pale Blue Dot
At Carl Sagan's urging, Voyager 1 turned its camera back toward the inner solar system and photographed Earth from roughly 6 billion kilometers (3.7 billion miles) away, a speck of light less than a pixel across in a sunbeam. The image, named the Pale Blue Dot, became one of the most widely reproduced photographs in the history of space exploration.
Location: Interplanetary space
Voyager 1 Enters Interstellar Space
Voyager 1 crossed the heliopause, the boundary where the sun's influence yields to the interstellar medium, becoming the first human-made object to enter interstellar space. NASA confirmed the crossing in September 2013 after analyzing plasma density data.
Location: Interstellar space
Voyager 2 Crosses the Heliopause
Voyager 2 crossed the heliopause, confirmed by NASA in 2019, becoming the second and only other human-made object in interstellar space. Because it carries a working plasma instrument that failed on Voyager 1, it provided the first direct measurements of the boundary from a second vantage point.
Location: Interstellar space
Engineering Rescues and Fading Power
Engineers patched Voyager 1's memory from more than 24 billion kilometers (15 billion miles) away after a corrupted chip had silenced the spacecraft for months, restoring communication. With their nuclear power sources decaying, the probes have progressively shut down instruments; both are expected to fall silent in the 2030s, after which they will drift through the galaxy indefinitely.
Location: Interstellar space